The present invention relates to a tire intended to be mounted on a two-wheeled vehicle and more particularly a motorcycle.
As in the case of all other tires, radialization of motorcycle tires is taking place, the architecture of such tires comprising a carcass reinforcement formed of one or two plies of reinforcement elements forming with the circumferential direction an angle which may be between 75xc2x0 and 90xc2x0, said carcass reinforcement being radially surmounted by a crown reinforcement formed at least of generally textile reinforcement elements.
Numerous crown reinforcement architectures have been proposed, depending on whether the tire is intended to be mounted at the front or the rear of the motorcycle. A first structure consists, for said crown reinforcement, of using solely circumferential cables, and said structure is more particularly used for the rear position. A second structure, directly inspired by the structures commonly used for tires for passenger cars, has been used to improve the wear resistance, and consists in using at least two crown plies of reinforcement elements which are parallel to each other within each ply but are crossed from one ply to the next, forming acute angles with the circumferential direction, such tires being particularly suited for the front of motorcycles. Said two crown plies may be surmounted radially by at least one ply of circumferential elements, which are generally obtained by helical winding of a strip of at least one reinforcement element coated with rubber. French Patent 2 561 588 describes such a crown reinforcement, with at least one ply, the reinforcement elements of which form with the circumferential direction an angle which may vary between 0xc2x0 and 8xc2x0, the elasticity modulus of such elements being at least 6000 N/mm2, and, arranged between the carcass reinforcement and the ply of circumferential elements, a shock-absorbing layer formed mainly of two plies of elements which are crossed from one ply to the next, forming between them angles of between 60xc2x0 and 90xc2x0, said crossed plies being formed of textile reinforcement elements having an elasticity modulus of at least 6000 N/mm2. 
In order to impart to a motorcycle tire excellent stability at high speed and excellent contact properties with the ground, EP 0 456 933 A1 teaches producing a crown reinforcement with at least two plies: a first ply, radially closest to the carcass reinforcement being composed of cables oriented at an angle of between 40xc2x0 and 90xc2x0 relative to the circumferential direction and the second ply, radially closest to the tread, being composed of cables wound in a helix in the circumferential direction.
U.S. Pat. No. 5,529,102 describes a motorcycle tire having crown plies which are formed of elements crossed at an angle between 16xc2x0 and 30xc2x0 and surmounted by a ply of reinforcement elements of aliphatic polyamide which may be radial. In order to increase the drive ability of a tire for the rear position of a motorcycle, U.S. Pat. No. 5,301,730 proposes a crown reinforcement composed, from the radial carcass reinforcement to the tread, of at least one ply of substantially circumferential elements and of two plies of elements which are crossed from one ply to the next, forming with the circumferential direction an angle which may be between 35xc2x0 and 55xc2x0, the ply of elements which are parallel to the circumferential direction being formed of elements of aromatic polyamide, and the plies of crossed elements of aliphatic polyamide.
Such tires make it possible, in addition to increasing drive ability, to preserve good speed properties, which makes said tires particularly suitable for sports competitions on a competition circuit. On the other hand, the use of aromatic polyamide as the material of the reinforcement elements of the two crossed plies in the crown reinforcement for motorcycles does not make it possible to obtain endurance of said crown reinforcement which is compatible with prolonged use on the road: the crossed reinforcement elements do not resist fatigue and the number of cycles effected being insufficient without it being possible to state the causes of such degeneration.
The object of the invention is to overcome such drawbacks by improving the endurance of motorcycle tires, without sacrificing the other properties which are necessary for satisfactory travelling on roads.
According to the invention, a motorcycle tire comprising a highly convex tread, joined by two sidewalls of low height to two beads, each bead being reinforced by an inextensible annular element around which is anchored a carcass reinforcement formed of textile reinforcement elements forming with the circumferential direction an angle of between 70xc2x0 and 90xc2x0, said carcass reinforcement being radially surmounted by a crown reinforcement formed of at least one ply of circumferential reinforcement elements, and two plies of reinforcement elements of textile material which are crossed from one ply to the next, forming with the circumferential direction angles of between 65xc2x0 and 85xc2x0, characterized in that said crossed elements are cables of aliphatic polyamide or polyester, the elasticity modulus of which is greater than 1,500 MPa, the circumferential elements being cables of aromatic polyamide, the elasticity modulus in tension of which is at least 10,000 MPa, the ply of circumferential elements being located radially between the carcass reinforcement and the two plies of crossed elements.
Reinforcement elements are said to be circumferential if they form an angle of between xe2x88x925xc2x0 and +5xc2x0 with the circumferential direction.
xe2x80x9cElasticity modulusxe2x80x9d of a reinforcement element refers to the modulus under tension of a reinforcement element taken from the vulcanized tire, said modulus being a secant modulus measured for a relative elongation of between 1% and 5%.
The characteristics and advantages of the invention will be explained more precisely in the following description, which refers to the accompanying drawing which illustrates an embodiment of the invention in an non-limitative manner.